Peroxide crosslinkable insulation compounds for extra high voltage (EHV) cable applications must be melt-filtered through fine screens during extrusion. U.S. Pat. Nos. 6,187,847 and 6,187,858 describe insulation formulations that have excellent properties, except that they suffer from peroxide instability during storage and exhibit high levels of water during crosslinking. U.S. Pat. No. 6,656,986 teaches that certain amine bases can mitigate these issues if they are included in the composition during extrusion. However, despite their excellent properties, manufacturing trials with the formulations described in U.S. Pat. No. 6,656,986 have identified a rapid pressure development due to fouling of the fine, e.g., less than 50 microns (μm), screen required to achieve EHV levels of cleanliness. This results in reduced run lengths and reduced yields of EHV grade, since long runs are required to achieve high EHV yields. This screen fouling phenomenon has not been appreciated in the prior art.
U.S. Pat. No. 8,455,580 describes compositions containing:                (A) Ethylene-based polymer;        (B) Polyalkylene glycol;        (C) 0.1-1% of a tertiary hindered amine stabilizer;        (D) Sulfur-containing hindered phenol antioxidant at 0.1% or greater;        (E) Peroxide; and        (F) Optional coagent.This disclosure does not teach use of a first sulfur-containing antioxidant having at least one —S(CH2)2CO2R group in combination with a phosphorus-containing antioxidant, and it does not teach the relative amounts of the antioxidants required by the present invention.        